1. Technical Field
The present invention relates to an automatic focusing arrangement which is adapted to drive a driven section of an interchangeable optical unit by a driving section in the main body of an optical instrument. For example, the optical instrument is a photographic camera with a camera body as the main body on which an interchangeable lens as the optical unit is mounted. In this case, the automatic focusing arrangement effects the automatic focusing through driving of the driven section in the interchangeable lens by the driving section provided in the camera body. The present invention also relates to the interchangeable optical unit and an instrument body coupled therewith which are adapted to automatically focus the optical unit.
2. Description of the Prior Art
For automatic focusing, an arrangement is possible in which a camera body is provided with a light receiving portion, an operation circuit, a motor, a motor driving control section, a driving shaft, etc., the focus condition of the image formed by an optical system of an interchangeable lens is detected by the light receiving portion, and when the detection indicates that an in-focus state has not been reached as yet, a judgement is made by the operation circuit as to the direction in which the optical system should be moved, in order that the operation circuit indicates the direction of movement for the focusing of the optical system.
In the above case, the indication of the direction is, in practice, substituted by the indication of the direction, in which the motor should be rotated, i.e. whether the motor should be rotated in the forward or reverse direction. Through rotation of a driving gear driven by the motor rotating in the indicated direction, a driven gear in the interchangeable lens is rotated for transmission of the rotation from a driven section to a focus adjusting section, and thus, the focusing is automatically effected.
However, interchangeable lenses to be driven by the motor as referred to above, in the arrangement as described above, are classified as various kinds, and for this reason, it is extremely difficult to equalize relationship between the driving directions of the focus adjusting section in the camera body and the driven section in the interchangeable lens to be rotated by the driving section for the automatic focusing, i.e. to unify the directions in which the driven section should be rotated for the focus adjustment of the optical system towards its terminal focusing position (for example, towards infinity focusing position).
More specifically, since the location of the driven section is determined in accordance with the diameters of the interchangeable lenses as designed for the convenience of manufacturing, the rotation given to the driven section is transmitted to an optical system shifting mechanism either through meshing between a pinion and an internal gear or through meshing between a pinion and an external gear, relying on the barrel structure. This difference in the manner of the transmitting the driving force causes the driving section to rotate in opposite directions i.e. in the forward and reverse directions relying on the lens type, for the focusing of the optical system in the same direction.
For eliminating the above inconvenience by normalizing the direction of the rotation of the driving section regardless of the lens type, it is necessary, for example, to limit the kinds of the interchangeable lenses to those having approximately the same range of diameters. If an interchangeable lens, in which the relationship between the driving directions of the focus adjusting section and the driven section is reversed is modified through an increase of the number of gears between the two sections such that the relation becomes normal it becomes bulky in size due to the complex gear mechanisms, with a consequent rise in the manufacturing cost, increase in the failure rate, and reduction of driving force transmission efficiency.
If the direction of a helicoidal screw in the focus adjusting section is reversed between the arrangement which provides the normal relationship of the driving directions of the driven section and the focus adjusting section and the arrangement which does not provide such normal relationship, there is a disadvantage that a lead cam (master cam) or the like of a helicoidal screw processing machine must be increased in number, with the simultaneous necessity for installation of a processing line corresponding to the direction of the screw. Moreover, if such reverse helicoidal screw system is employed for an interchangeable lens provided with both systems for automatic focusing operation and manual focusing operation, the directions of operation for the manual focusing are different according to the lens models, so that the user may be perplexed in determining the proper directions for focusing during actual photographing and may lose the opportunities for shooting by the delay of the focusing operation.
Furthermore, if the orientations of the driving directions for the focus adjusting section in the interchangeable lens are not normalized, it will be impossible to effect focusing for some kinds of camera bodies. It is possible to have a driven section of an interchangeable lens to be driven experimentally before actual automatic focusing so that the direction of the focus driving of a focus adjusting section of the lens by the driven section can be detected and to start the actual automatic focusing with the detected result considered. However, there will result the inconvenience such as an extreme increase of time required for the focusing, etc.